Schistosomiasis is an acute and chronic disease caused by parasitic worms. According to the WHO, it affects almost 240 million people worldwide, and more than 700 million people live in endemic areas. Several million people all over the world suffer from severe morbidity as a consequence of schistosomiasis. Praziquantel is currently the only recommended drug for infection and disease caused by the species of schistosome infecting humans.
Praziquantel (PZQ) was registered, approved and commercialized in the beginning of the 1980's as a racemic mixture. However, it has turned out that only the (R)-enantiomer is active (eutomer) (P. Andrews, H. Thomas, R. Pohlke, J. Seubert Medical Research Reviews 3, 147(1983)).

Racemic Praziquantel has a repugnantly bitter taste. This leads to acceptance issues—in particular in the treatment of young children. In addition to the difference in activity, the (R)-Praziquantel eutomer is also considered to have a less bitter taste than the (S)-Praziquantel distomer (T. Meyer et al. (2009) PLoS Negl Trop Dis 3(1): e357). Thus, there is a desire for an economical manufacturing process that is suitable to prepare enantiomerically enriched or preferably even pure (R)-Praziquantel.
During the past decades, numerous attempts were made to develop a manufacturing process for (R)-Praziquantel or its analogues. These attempts can be divided into two groups, firstly enantioselective synthesis routes, and secondly methods producing a racemic mixture in combination with chiral resolution. Given that the latter approach necessarily involves additional process steps, a process leading directly to (R)-Praziquantel might principally be more attractive. However, identifying a suitable enantioselective route of synthesis that is economically attractive has proven very difficult. The pursuit of such a synthesis as well as other methods of economically manufacturing (R)-Praziquantel is still ongoing.